Add domain cache invalidation and new domain fetching logic

- Implemented `invalidate_domain_cache` function to clear cached domain data.
- Updated `get_td_domain` to utilize caching for domain retrieval.
- Modified `main_menu` and `uninstall_menu` to invalidate cache when necessary.
- Enhanced watchdog logic to clear domain cache on failure.

src/app_config.sh

@@ -108,6 +108,8 @@ uninstall_menu() {
 			version_menu
 			;;
 		"E)")
+			cachedMenuDomain=''
+			invalidate_domain_cache
 
 			if ! [[ "$0" =~ .*"/usr/bin/nightscout-tool" ]]; then
 				okdlg "Opcja niedostępna" \

src/app_main.sh

@@ -95,6 +95,8 @@ main_menu() {
 
 		case $CHOICE in
 		"S)")
+			cachedMenuDomain=''
+			invalidate_domain_cache
 			status_menu
 			;;
 		"P)")

src/lib.sh

@@ -24,6 +24,8 @@ WATCHDOG_TIME_FILE=/srv/nightscout/data/watchdog_time
 WATCHDOG_LOG_FILE=/srv/nightscout/data/watchdog.log
 WATCHDOG_FAILURES_FILE=/srv/nightscout/data/watchdog-failures.log
 WATCHDOG_CRON_LOG=/srv/nightscout/data/watchdog-cron.log
+DOMAIN_NAME_FILE=/srv/nightscout/data/domain_name
+DOMAIN_UPDATE_TIMESTAMP=/srv/nightscout/data/domain_update_timestamp
 SUPPORT_LOG=/srv/nightscout/data/support.log
 EVENTS_DB=/srv/nightscout/data/events.env
 UPDATE_CHANNEL_FILE=/srv/nightscout/data/update_channel

src/logic_app.sh

@@ -22,7 +22,7 @@ update_logto() {
 	fi
 }
 
-get_td_domain() {
+get_td_domain_from_api() {
 	local MHOST=$(hostname)
 	if ! [[ "$MHOST" =~ [a-zA-Z]{2,16}[0-9]{3} ]]; then
 		MIKRUS_APIKEY=$(cat "/klucz_api")
@@ -35,6 +35,63 @@ get_td_domain() {
 	curl -sd "srv=$MHOST&key=$APIKEY" https://api.mikr.us/domain | jq -r ".[].name" | grep ".ns.techdiab.pl" | head -n 1
 }
 
+invalidate_domain_cache() {
+	echo "" >"$DOMAIN_UPDATE_TIMESTAMP"
+	echo "" >"$DOMAIN_NAME_FILE"
+}
+
+get_td_domain() {
+	local domain=""
+	local cache_age=999999
+	local now
+	now=$(date +%s)
+
+	# Check if we have a valid timestamp and cached domain
+	if [[ -f "$DOMAIN_UPDATE_TIMESTAMP" && -f "$DOMAIN_NAME_FILE" ]]; then
+		local last_update
+		last_update=$(cat "$DOMAIN_UPDATE_TIMESTAMP" | tr -d '[:space:]')
+		if [[ -n "$last_update" && "$last_update" =~ ^[0-9]+$ ]]; then
+			cache_age=$((now - last_update))
+		fi
+	fi
+
+	# Use cache if it's less than 24 hours old and contains a valid (non-empty) domain
+	if ((cache_age < 86400)); then
+		local cached_domain
+		cached_domain=$(cat "$DOMAIN_NAME_FILE" 2>/dev/null | tr -d '[:space:]')
+		if [[ -n "$cached_domain" ]]; then
+			if [[ "$UPDATE_CHANNEL" == "develop" || "$FORCE_DEBUG_LOG" == "1" ]]; then
+				echo "domain: from cache (${cache_age}s old): $cached_domain" >>"$DEBUG_LOG_FILE"
+			fi
+			echo "$cached_domain"
+			return
+		fi
+	fi
+
+	# Cache miss, stale, or empty cached value - fetch from API
+	local raw_domain
+	raw_domain=$(get_td_domain_from_api)
+	domain=$(echo "$raw_domain" | tr -d '[:space:]')
+
+	# Save result to cache; empty result is also saved so it can be detected as
+	# "unknown" - empty cached value causes re-check on every subsequent call
+	echo "$domain" >"$DOMAIN_NAME_FILE"
+	if [[ -n "$domain" ]]; then
+		echo "$now" >"$DOMAIN_UPDATE_TIMESTAMP"
+		if [[ "$UPDATE_CHANNEL" == "develop" || "$FORCE_DEBUG_LOG" == "1" ]]; then
+			echo "domain: freshly retrieved from API: $domain" >>"$DEBUG_LOG_FILE"
+		fi
+	else
+		# Clear timestamp so next call always retries the API when domain is empty
+		echo "" >"$DOMAIN_UPDATE_TIMESTAMP"
+		if [[ "$UPDATE_CHANNEL" == "develop" || "$FORCE_DEBUG_LOG" == "1" ]]; then
+			echo "domain: API returned empty result, cache cleared" >>"$DEBUG_LOG_FILE"
+		fi
+	fi
+
+	echo "$domain"
+}
+
 get_domain_status() {
 	local domain=$(get_td_domain)
 	local domainLen=${#domain}

src/logic_watchdog.sh

@@ -261,6 +261,7 @@ watchdog_check() {
 
 		else
 			WATCHDOG_STATUS="domain_failed"
+			invalidate_domain_cache
 		fi
 
 	else